Network devices may be connected with conventional interconnection subsystems such as, for example, a small computer system interface parallel interconnect bus ("SCSI bus"), a SCSI Fibre Channel bus, or an Ethernet based local area network. Devices utilizing a SCSI bus, for example, are configured to comply with the SCSI protocol (e.g., SCSI-1, SCSI-2, or SCSI-3, among others), the specification of which is discussed in "Information Technology--SCSI-3 Architecture Model" X3T 10 994D Revision 18, from the American National Standards Institute ("ANSI", located at 11 West 42nd Street, New York, N.Y.) and in "SCSI-3 Architecture Model (SAM)" X3.270:1996, also available from ANSI. Both such publications are incorporated herein, in their entirety, by reference.
Initiator devices (i.e., devices connected to a bus requesting access to other devices connected to the bus, commonly referred to as "initiators") on a SCSI bus may access other devices (i.e., devices connected to the bus and being accessed by initiators, commonly referred to as "targets") on the bus in accordance with the SCSI protocol. The SCSI protocol specifies that an initiator requesting access to a target must transmit an access message to the target specifying an initiator identifier identifying the initiator, a target identifier identifying the target, and a logical unit number ("LUN") identifying the portion of the target device to be accessed ("logical unit"). The initiator identifier and the target identifier typically identify the physical location (i.e., physical address) of the initiator/target on the bus (e.g., the identification number of the port on the SCSI bus).
As is known by those skilled in the art, different bus protocols set different limits on the maximum number of logical units within a single target that may be accessed by an initiator. For example, a maximum of eight logical units in a single target may be accessed by an initiator connected to a bus system that is utilizing the SCSI-1 and SCSI-2 protocols. Accordingly, the initiator on such bus system may access no more than eight logical units per target. Other logical units in the target thus undesirably are not visible to the initiator. In a similar manner, a maximum of 2.sup.64 logical units are visible to an initiator when using the SCSI Fibre Channel protocol on conventional systems.
One system implementation utilizing a SCSI bus, for example, may include a target controller operating a central disk array that is used to store information for several host computer systems. Accordingly, in a disk array having hundreds of disks that each operate as separate logical units, bus systems using the SCSI-1 or SCSI-2 bus protocol grossly underutilize the disk array because only eight of the disks in the array may be accessed.
There also are privacy problems with conventional targets such as, for example, a disk array. Specifically, the LUN in an access message may specify one or more disks in the disk array to store information from an initiator host computer system. In many such prior art bus systems, however, depending upon the bus protocol, the entire disk array is accessible (via the target controller) by all of the host computers connected to the bus, thereby limiting the privacy of the files stored in the disk array.
The art has responded to this privacy problem by partitioning disk arrays, for example, into a plurality of partitions, assigning a different array port (i.e., bus connection points) and target controller to each partition, and connecting an independent bus to each array port. Accordingly, a partition is accessible by those initiators only that are on the bus that is connected to the associated array port. This solution therefore requires that the disk array have the same number of ports as array partitions, as well as an equal number of busses. This requirement necessarily increases the ultimate cost of manufacturing and utilizing such network system.